This invention relates generally to a tokamak reactor system and more particularly to a modular tokamak magnetic system.
The magnetic system of a tokamak fusion reactor consists of toroidal magnetic field (TF) coils, poloidal magnetic field (PF) coils, and ohmic heating (OH) coils. Generally, there are two approaches in designing tokamak reactor magnetic coil systems. One approach is to place the PF and OH coils inside the TF coil bore. The other approach is to place the PF coil outside the TF coils and the OH coils in the central core.
In the first approach, the PF and OH coils are in close proximity to the plasma, minimizing the current required in these coils. The disadvantage to such a system is that the PF and OH interlock with the TF coil. This interlocked coil design poses a difficult maintenance problem for superconducting systems. The maintenance problem is so extreme that the second approach is usually considered in most reactor designs. The second approach however, poses different kinds of problems. First, the PF coils are far away from the plasma. Thus, a very large current is required in the PF coils to shape and control the plasma equilibrium configuration. Second, for small aspect ratio tokamaks, the central core space is very limited, necessitating a vary large current in the OH coil to produce a reasonable flux swing. Thus, the total energy stored in the PF and OH systems would be in the multigigajoule range for a typical power reactor. A further disadvantage to this design is the large overturning moment generated by the large current in the PF coils. Generally, the advantages and disadvantages of each approach are summarized below in Table 1.
TABLE 1 ______________________________________ Comparison of the Advantages and Disadvantages of External and Internal PF and OH Coil Systems Cur- Plasma Overturning Main- rent Control Moment tenance ______________________________________ Internal PF Coils low good low poor External PF Coils high poor high good Internal OH Coils low -- low poor External OH Coils high -- high good ______________________________________
It is clear that the only drawback of an internal system is the problem of maintenance. Finding a solution to this problem would make the internal system a very attractive approach. For a copper device, the TF coil can be made into many sections if plate construction is used. However, the maintenance problem is still difficult if the sections are joined by bolts. This problem can be resolved by using pressure joints with locking rings and keys, as disclosed by Yang, et al., Fusion Technol 8, 838 (1985). The OH and PF coils can now be located inside the TF bore. Maintenance of these coils and the vacuum vessel can be accomplished by lifting the entire top conductor of the TF coils. Such a design makes maintenance of all internal parts possible, however, it is not a simple task to lift and reassemble the entire top. Also, at present there is no known method of making joints for superconductors. This kind of segmentation method for superconducting magnets will not be available in the foreseeable future. Therefore, making superconducting PF magnets utilizing the segmentation method and pressure joints is not feasible.
In order to make the internal PF and OH systems maintainable, it is essential to find a modular system for the PF and OH coils.
Therefore in view of the above, it is an object of the present invention to provide a tokamak system which can be easily maintained.
It is another object of the present invention to provide a tokamak system which minimizes the current needed to shape and control the plasma equilibrium configuration while remaining easy to maintain.
It is another object of the present invention to provide a modular OH coil system for a tokamak.
It is a further object of the present invention to provide a modular PF system for a tokamak.
It is still another object of the present invention to provide a tokamak reactor consisting of interlocking modules.
Additional objects, advantages and novel features of the invention will be set forth, in part, in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations, particularly pointed out in the appended claims.